lpg pipeline blowdown 1

[Essex57]

Would the forum members preference be to blowdown a 12" x 100ft liquid LPG line (after closing SDVs) within a plant, in the event of an emergency - or would the preference be to shut in the volume and protect with fireproofing such as Chartek

 

[Homayun]

Well, we are talking about only 2 m3 (70 ft3), so it's relatively very small volume. If the emergency is not fire, I would'nt bother depressurising it. But what are you going to do with the vessle upstream of this pipe, where the LPG is coming from?
I would guess this LPG stream is an overhead stream of a tower, in which case you would probabely want to depressurise the whole column. So you could also take this line with the same column and depressurise at the same time.

 

[EGT01]

Essex57,

If you are talking about overpressure protection for a fire event, I would point out that fireproofing will not prevent an overpressure concern. It will reduce the amount of heat input to the system and reduce the temperature that the pipe wall will directly see. You would still need some other means of limiting the pressure as the liquid temperature increases.

 

[MortenA]

When dealing with LPG (Liquid Petroleum Gasses) you have a liquid where the initial blowdown is very limited - because its a liquid. If you can't drain it then the volume that will mean than only very limited amounts of liquid will need to be removed to reduce the pressure. However as the pipe heat up (and as EGT01 noted it will heat up) then the LPG will boil and if the low pressure should be maintained then an amount of vapous equal to the heat influx divided by the heat of evaporation for the LPG will need to escape.

This is a fairly trivial set of calculations that needs to be performed in order to asses the sizing of either a blowdown valve or a PSV. You should however also consider that while vapours may be generated it could be that it is liquid that need to be relieved at the valve.

If you only will consider a limited fire with some limited duration then maybe fireinsulation will be enough to ensure that within this time the pipe does not get so hot that the vapour pressure of the LPG exceeds the MAWP of the pipeline?

Best regards

Morten